Wet Weather Raises Concern For N Losses

Wet Weather Raises Concern For N Losses

Above normal rainfall across Iowa and much of the Corn Belt has some growers wondering if they have enough nitrogen left in the soil for their corn crop. Here are in-season application tips.

Recent rainfall across much of the Corn Belt has some growers wondering if they have enough nitrogen left in the soil for their corn crop. Agronomists say growers need to evaluate fields and, in some cases, develop a nitrogen rescue strategy.

"Each year presents new environmental challenges," says John Shanahan, Pioneer agronomy research manager. "Nitrogen is the single most expensive input, which means there are numerous reasons to get it right. That is, applied in the right amount, at the right timing, on the right acres. Growers who don't apply enough nitrogen risk reduced yields."

Early-season nitrogen stress creates irreversible yield loss. According to university research, for each day of moisture saturation, 3% to 4% of the nitrate in the soil is lost.

If your corn is running short of N, consider a sidedress application

"Corn requires nearly half of its total nitrogen supply between V8 growth stage and tasseling," Shanahan says. "Pioneer recommends side-dressing nitrogen between V4 and V8, allowing a safety margin for weather and soil conditions that delay nitrogen application or the movement of nitrogen to the roots."

Using the late spring soil nitrate test is a useful tool for evaluating the amount of nitrogen in fields. Testing soils at least 12 inches deep can help indicate the amount of nitrogen currently available to the corn plant. You need to pull these soil samples when the corn is 6 to 12 inches tall. Another option is to use optical sensors mounted on nitrogen application equipment.

Optical sensors emit modulated light of the appropriate wavelength onto plants and measure how much is reflected back to the sensor. This measure of "crop greenness" correlates with the plant chlorophyll content. Estimating chlorophyll content also estimates crop nitrogen status.

"A grower also can estimate nitrogen by answering some key questions," Shanahan says. "When was the nitrogen fertilizer applied, what form was used, how much was applied and what have field conditions been following the application." Also, did you apply manure to this ground?

Because N fertilizer is expensive, sidedressing is a great option

If a grower determines his or her corn crop is nitrogen deficient, an additional side-dress or rescue nitrogen application is an option.

"Because nitrogen is so expensive, side-dressing is a great option," Shanahan says. "Spreading applications throughout the growing season reduces risk. If wet spring conditions result in nitrogen losses, growers can increase their sidedress nitrogen application rates. If warm temperatures and moderate rainfall result in high nitrogen mineralization and a nitrogen-sufficient crop, growers can reduce the sidedress rates. They can apply less nitrogen per acre."

Growers who need a rescue application can apply nitrogen with a high-clearance sprayer using ammonium nitrate. Broadcasting urea is another nitrogen application option.

Plan equipment and nitrogen sources for in-season application

"Growers need to evaluate what type of equipment and nitrogen sources are available," Shanahan says. "If a grower is going to make in-season applications, he or she needs to have a plan in place and work with their local applicator. Once the crop is about knee-high, ensuring sufficient nitrogen is a priority."

Pioneer is developing nitrogen-efficient corn hybrids. Research focuses around improving the yield of corn using native and transgenic genes. In addition to improving the utilization of nitrogen, researchers are working to lower the level of nitrogen inputs while maintaining yield. "We look at several ways to use nitrogen, through genetics and management techniques," Shanahan says. "Enhancing nitrogen utilization is beneficial both economically and environmentally."

For more information on in-season nitrogen applications, contact your local Pioneer professional or visit www.pioneer.com/agronomy.

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